(i) Field of the Invention
The present invention relates to a process and a plant for the treatment of products, in particular of food products, with ozonized water, the aim being in particular, depending on the case, to bleach, disinfect or deodorize the products thus treated.
(ii) Description of the Related Art
It is known that the literature relating to the treatment with ozone of articles such as medical instruments or else products such as food products, in instruments or else products such as food products, in particular in the field of washing food products with ozonized water (seafood, such as fish or Crustacea, but also fruit and vegetables, and the like), is extremely rich; reference may be made in particular to the documents Fr-385,815, EP-294,502, Fr-797,928, Ca-2,102,362 or U.S. Pat. No. 4,559,902.
One of the applications which is highly promising today is actually the washing of food products with ozonized water, in particular the washing of fruit and vegetables or seafood. These washing operations with ozonized water have been very particularly proposed as replacement for washing with chlorinated water, chlorine being progressively subject to very severe restrictions in this industry, indeed even banning pure and simple.
In these known processes for washing with plain water or optionally chlorinated water, it is known that the effectiveness of the washing is related to the energy employed and consequently the water in the tank is commonly stirred, typically by the injection of compressed air into the solution. The role of this stirring is in particular to detach dirt and other organic loads from the products to be treated but also to replace the disinfectant molecules at the surface of these products, in order to thus enhance disinfectant/product transfer and to improve the effectiveness of the washing.
Studies brought to a successful conclusion by the Applicant Company have allowed it to be shown that, in the case of washing with ozonized water, such stirring by the pneumatic route is undesirable, in so far as it promotes phenomena of degassing and thus the loss of a portion of the ozone dissolved in the washing water.
The stirring conditions to be put in place in the case of washing with ozonized water are in fact, according to these studies, even more critical and the following reasons may in particular be put forward for this:
ozone is a much more powerful oxidizing agent than chlorine and it results in a much greater xe2x80x9cexhaustionxe2x80x9d when brought into contact with the products. This exhaustion phenomenon is characterized, for the majority of products, by a sudden decrease in the content of ozone in the solution in the first contact, which decrease is related to the organic load of the products and to their exchange surface area (for example, the case of cruditxc3xa9s, where the exchange surface area is greatly increased because of the divided state);
coupling in this instance with efficient stirring is then even more crucial (homogenization of ozone in the tank).
The present invention is targeted in particular at solving the above-mentioned technical problems.
The present invention relates generally to a process for the treating of a product comprising the steps of:
contacting the product with a solution of ozonized water subjected to stirring during all or part of the contacting, wherein all or part of the stirring is hydraulic in origin;
recirculating at least a portion of the solution contacted with the product to one or more points where the contacting step occurs so as to establish turbulent water conditions capable of allowing achievement of a sufficient contact time between the product and the ozone dissolved in the water to attain a required level of treatment.
Preferably, the process for the treatment of a product according to the invention comprises a stage in which the product is brought into contact with a solution of ozonized water in at least one treatment tank fed with ozonized water, the solution being subjected to stirring during all or part of the contacting phase. All or part of the stirring is hydraulic in origin and the recirculation of at least a portion of the solution in the tank is established in order to reintroduce this recirculated solution at one or more points in the structure of the tank, making it possible by this reintroduction to establish, within the tank, turbulent water conditions capable of allowing the achievement of a sufficient contact time between the product and the ozone dissolved in the water to attain the required level of treatment.
The process according to the invention can also adopt one or more of the following characteristics:
the turbulent conditions are obtained by arranging a degree of recirculation of water in the tank corresponding to 5 to 50 volumes of the tank per hour;
the content of ozone dissolved in the ozonized water feed of the treatment tank is between 0.1 and 20 ppm and more preferably between 0.5 and 15 ppm;
the content of ozone dissolved in the solution present in the treatment tank is regulated within the range of 0.1 to 10 ppm and more preferably within the range of 0.5 to 5 ppm;
the at least one treatment tank is substantially parallelepipedal in shape, thus defining a front wall of the tank, side walls and one or more walls forming the base of the tank, the inlet or inlets for recirculated solution in the structure of the tank then being positioned according to one or more combinations of the following configurations:
(i) the inlet or inlets for recirculated solution are composed of at least one linear sequence or series of injection nozzles emerging in the tank on at least one of its side walls;
(ii) the inlet or inlets for recirculated solution are composed of at least one linear sequence or series of injection nozzles emerging in the tank on its front wall;
(iii) the inlet or inlets for recirculated solution are composed of at least one knife emerging in the tank on the wall or walls forming the base of this tank;
the inlet or inlets for recirculated solution are composed of at least two linear sequences or series of injection nozzles emerging in the tank on at least one of these side walls, the linear sequences or series being operated sequentially in order to obtain the required contact time;
the inlet or inlets for recirculated solution are composed of at least two linear sequences or series of injection nozzles emerging in the tank on its front wall, the linear sequences or series being operated sequentially in order to obtain the required contact time;
the flow rate of recirculated solution injected into the tank is adjusted in order to control the progress of the products in the tank and thus to obtain the required contact time.
The present invention is based on the achievement of stirring of hydraulic type of the ozonized water in the treatment tank with the help of inflows of ozonized water recirculated from the tank which refeed the tank at chosen positions in this tank, so as to set up turbulent conditions inside the solution (which must be understood in that the tank does not have regions of water stagnation or regions with a zero velocity of displacement of the water), these turbulent conditions making it possible to achieve the sufficient contact time between the product and the ozone dissolved in the water in the tank to attain the required level of treatment.
It is also understood that the xe2x80x9ctreatmentxe2x80x9d with ozonized water according to the invention is targeted not only to the product under consideration but also according to the specifications demanded by each specific site of use, at carrying out one or more of the actions from the following actions: bleaching, disinfection or deodorization of the product.
Although, in the above and the following, the invention is very particularly illustrated in the case of food products, it is understood that it applies much more broadly to other products or articles, such as medical items and equipment. The term xe2x80x9cproductxe2x80x9d or xe2x80x9carticlexe2x80x9d will then be used without distinction.
Still by way of illustration, in order to give an example of the notion of xe2x80x9csufficient contact time between the product and the ozonexe2x80x9d according to the invention, consideration may be given to the example of food products and more specifically of crudites, such as carrots, for which the quality of the products after treatment will be evaluated by a measurement of the TMAF (Total Mesophilic Aerobic Flora, often known in this industry as xe2x80x9cTotal Floraxe2x80x9d).
In addition to water and ozone, the aqueous treatment solution according to the invention can comprise, according to the application under consideration, additives such as acids or bases, the role of which can be in particular to adjust the pH of the medium.
On considering, in what follows, the specific case of food products, it is known that plants for the washing of food products conventionally include at least one washing tank but commonly several of these washing tanks, the water from at least one of these tanks being chlorinated, for example. According to the present invention for washing products with ozonized water, each treatment tank can therefore be the only washing tank of a line or else can be preceded or followed on the line by one or more tanks for washing with water, the water optionally comprising an additive. Each situation will depend, as will clearly appear to a person skilled in the art, on the type of product and on the initial state of cleanliness of the products treated.